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Tuesday, August 27, 2013

There is a natural and wonderful symmetry to many natural objects and echinoderms have always had a certain appeal to folks with artistic natures. Their skeletons are pentameral and often have no shortage of patterns and visually interesting processes. Go here to seem my SEM odyssey of the urchin test!

Sea urchins are no exception to this-and everyone I know who has ever found an intact sea urchin (or sand dollar) test on the beach is always delighted. A "test" is the name of a sea urchin skeleton. They don't have "shells".

Here's a nice example of a cidaroid sea urchin test. The spines attach to the "knobs" (called bosses) that are present on its surface.

sea urchin test by Rainy City

Today, I thought I would present some of the many delightful examples that many of these tests have found their way into the creative processes of the wonderful artists on the Internet! Then compare below with some examples of sea urchin tests with their own innate artful patterns!

Cidaroid Urchins a la Warhol! by Calypso985

A stunning underlit cidaroid urchin test by Mark Bolles

A neat repeating Urchin Spiral by Jeff Kreulan

"Red Tide" part of an art exhibit featuring urchins with a distinctive presentation. Pic by Selene Vomer

Amazingly, the patterns? ARE NATURALLY OCCURRING. Those are on the test under the spines and all of the other structures and skin on the surface! They don't disappear after the animal has died. They are ingrained in the mineral structure of the test.

Our story begins with an overview of two unusual and quite tiny starfish! Some details:

Occur in Tasmania (Southern Australia)

Two species, Parvulastra vivipara and P. parvivipara occur on rocks and surrounding areas.

One of those starfish, P. parvivipara is among the world's smallest adult sea stars.

Indeed! Look how cute and tiny they are!

Image by Nuytsia@Tas

But the truth is that these tiny little starfish have all kinds of shocking sex secrets!1. Both Species of Parvulastra are self-fertilizing hermaphrodites.
I have written about similar species in the same genus (Parvulastra) here.
Yes, that's pretty much self explanatory. Individuals are simultaneously both male and female AND if need be they can fertilize themselves.

They typically have between 6 to 8 female gonads and 1 predominantly male gonad. However the amount of sperm present would not be expected in those species which are exclusively self-fertilizers-so SOME outcrossing (ie sex with other individuals) does occur.

So, eventually, those little baby starfishes have to leave the comfort of the mother's body cavity. This happens when they reach about 25-30% of the parent's body diameter.

The downside of having brooded juveniles is that they tend not to go very far from the adult. In other species, the larvae would be dispersed over wide distances but here, they are retained or crawl away, staying near the parent..

Eventually, they exit via openings in the abactinal body wall called GONOPORES.

Life is harsh and these starfish know it better than anyone. The gonads in these animals are pretty small which implies that food for the juveniles isn't really enough to keep them sustained on their own..

So, as soon as the brooded juveniles develop a mouth they begin feeding on their siblings in the body cavity! In the specimens examined several of the larger brood individuals, which contained traces of the smaller ones in their gut contents in addition to other observations..

Several possible reasons may motivate the departure of the smaller juveniles from the brood space. Temperature or any number of factors.

Byrne speculated on one reason that juveniles may vacate in order to avoid being fed upon by their larger siblings.. Here is a cartoon supplied by the Echinoblog Art Dept. which illustrates this notion (which to be honest was mentioned as only one sentence by Byrne in her paper).

Ultimately, then we see various brooded juveniles vacating the brood space via the gonopores (which flex and open) with the tiny juveniles emerging on the surface and eventually moving away...

Fr. Byrne 1996, Fig. 8b

Thanks to the intragonadal cannibalism however, sometimes you get a REALLY big one which continues to grow INSIDE the parent. Ultimately reaching a size at which it cannot physically escape on its own..

There was nearly a complete loss of genetic diversity among all populations of Parvulastra and given the very restricted geographic range of these species+ the very limited way they can disperse their juveniles across wide distances there's little potential for populations to expand.

Thus, these live-brooding species with little to no gene flow display a high risk of extinction

So, there is serious concern about these species to withstand any kind of temperature or climate shift. The populations of these live-bearing starfish species is pretty small and pretty restricted. Potentially any kind of abrupt habitat change could wipe out these starfish with these unusual life modes..

The Okeanos Explorer has been to Indonesia and many other locales, such as the Galapagos and the deeps off the Caymans, but is currently operating off the east coast of North America, surveying and studying a series of deep-sea canyons and seamounts as seen here. Those on the legs I've seen (2nd leg?) are in white arrows...

What's even more fantastic? Many deep-sea biologists, some world experts in the field, are actually listening in via phone, or via internet forums. I'm one of the world's experts on starfish and I'm monitoring via Twitter (@echinoblog) and via conference call.

Each day of the expedition can go anywhere from 5 to 7 hours. So there's a LOT of footage. So here.. I present some of the highlights of new discoveries and neat, weird deep-sea animals from the last few days of video footage.

There's still more to come and undoubtedly, I've undoubtedly missed some but this gives you a nice overview of new discoveries and awesome stuff from the 1000+ meter deeps off the east coast of North America!

These animals are heavily studied and are important to ecologists as well as physiologists and even scientists researching astrobiology (those that explore how life on other planets originated in extreme habitats)

Cold Seep habitats are unusual and when found, they are often monitored by the scientific community for study because of their potential importance.

Parasites? Commensals Part of the animal? A new species? MANY questions!

Sea Spiders aka Pycnogonids crawl on deep-sea corals and other cnidarins
Here's one on a sea pen

Another crawling on some deep-sea coral

Weird & Rarely Seen Deep-sea starfish species!
This starfish, called Pythonaster, is known from fewer than 6 specimens in the entire world. This is the 2nd time this animal has been observed alive and the FIRST time it has been observed alive in the Atlantic.

Here is a plate of this animal from the HMS Challenger Expedition, which described it in 1889!!

This starfish, Neomorphaster, is better known to scientists, but seeing it alive like this? That's not something that happens often.

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
Need to hire an invertebrate zoologist/marine biologist? Please contact me!